Glioblastoma in New Zealand: A retrospective cohort analysis post WHO CNS 5

Glioblastoma represents one of the deadliest primary brain cancers and has undergone frequent diagnostic classification changes. New Zealand has a relatively small population facilitating a national individual patient cohort analysis. This study looks at glioblastoma diagnosis, treatment including radiotherapy and outcomes across New Zealand for a calendar year.

Patients diagnosed with glioblastoma according to the 2021 WHO guidelines were identified across the five neurosurgical units in New Zealand between 01/01/2021-31/12/2021. A total of 184 patients were included.

Crude overall incidence was 3.6 persons per 100,000, with a reduced age-standardised incidence in indigenous Māori at 2.5 diagnoses per 100,000 versus 3.8 per 100,000 for non- Māori was identified. Median overall survival (OS) was 10.6 months and did not differ across units (p = 0.782) or by ethnicity (p = 0.653). Gross total resection was associated with longest OS of 20.0 months, whilst OS after biopsy was only 4.0 months (p < 0.001). Mean time to radiotherapy (TTR) was on average 41 days (interquartile range: 33 - 49 days), and there was no significant difference in OS in patients with delayed radiation therapy beyond 8 weeks (14.6 % of patients) compared to those with earlier radiotherapy (p = 0.538). However, identification of rapid early progression was associated with worse OS (p = 0.030). Patients who received conventionally fractionated chemoradiotherapy had a median OS of 19.1 months (95 % confidence interval: 15.3---22.8 months), whilst those patients ≥ 65 years old who received hypofractionated chemoradiotherapy had a median OS of 12.6 months (95 % confidence interval: 7.6 - 17.6 months) in keeping with the landmark clinical trial outcomes of 14.6 months (95 % confidence interval: 13.2 - 16.8 months) median OS in the 2005 Stupp trial and 9.3 months (95 % confidence interval: 8.3 - 10.3 months) median OS in the 2017 Perry trial respectively.

This study is the first national cohort for glioblastoma patients diagnosed according to the 2021 WHO guidelines across a calendar year. There was a difference in the age-standardised incidence in Māori and non-Māori populations but with no difference in OS. We identified New Zealand population OS rates that match international cohorts and practice changing clinical trials, and we found no difference in OS depending on TTR, ethnicity or treating unit.